Question

write a short paragraph in which you differentiate between the terms pili and fimbriae.

This is for a microbiology course.

Answer 1

Both Fimbriae and Pili are filamentous structures composed of protein that extend from the surface of a bacterial cell. But they are different in each other in the following aspects-

Fimbriae are bristle like short fibres occurs on the surface of bacteria. Whereas pili are long hair like tubular microfibres like structures present on the surface of bacteria. Fimbriae are present on both Gram positive and Gram negative bacteria but Pili are present only on some Gram negative bacteria. Fimbriae are made up of fimbrillin protein, Pili are made up of pilin protein. Fimbriae are comparatively shorter in length ( 0.03 to 0.14 µm) than pili and pili are longer (0.5 – 2 µm) fimbriae. Fimbriae are evenly distributed on the entire surface of the cell, Pili are randomly distributed on surface of the cell. The total number of fimbriae per cell range from 200 – 400, which is more than pili which are only 1- 10 in number in cell. The formation of fimbriae is controlled by the genes present in the nucleoid region of bacteria. Whereas, The formation of pili is controlled by the gene present in plasmids. Fimbriae are a solid structure, but Pili are hollow tubular structures. The fimbriae are comparatively thinner in their diameterir, pili are thicker than fimbriae. Fimbriae are flexible, pili are rigid.

The main function of fimbriae is surface attachment i.e. cell adherence. The function of pili is gene transfer by bacterial conjugation and attachment(sex pili). Fimbriae do not play any role in conjugation.

Fimbriae do not have any role in bacterial mobility,but some pili such as Type IV pili show the twitching type of mobility.

The majority of pili act as the receptors for some virus, but fimbriae do not.

Bacteria like Salmonella typhimurium, Shigella dysenteriae possess fimbriae. Shigella uses its fimbriae to attach to the intestine and then produces a toxin that causes diarrhea.

Escherichia coli, Neisseria gonorrhoeae, Pseudomonas possess pili. Neisseria uses pili to attach to the urogenital and cervical epithelium when it causes disease gonorrhoea.